1. Field of Invention
The present invention relates generally to the field of testing hydrocarbon-bearing formations, and more particularly to methods, systems and apparatus useful in such operations.
2. Related Art
Coiled tubing is a technology that has been expanding its range of application since its introduction to the oil industry in the 1960's. Its ability to pass through completion tubulars and the wide array of tools and technologies that can be used in conjunction with it make it a very versatile technology, and this versatility is the core of this invention. Recent advances in coiled tubing allow real-time control of downhole equipment, transmission of measurement data and isolation of individual zones within the reservoir.
Typical coiled tubing apparatus includes surface pumping facilities, a coiled tubing string mounted on a reel, a method to convey the coiled tubing into and out of the wellbore, and surface control apparatus at the wellhead. During the spooling process the coiled tubing is plastically deformed as it comes off the reel and is straightened by the injector as it is run into the well. The coiled tubing will expand slightly under the influence of differential pressure.
One typical method of testing and evaluating reservoirs is drill-stem testing. Another is wireline testing. Reservoir boundaries, skin and permeability information are needed to optimize production and reservoir development. Problems arise because of commingled flow.
Unfortunately, drill-stem testing requires removing existing completions, and includes the cost of bringing a rig to convey individual sections of drillpipe. Drill-stem testing also does not lend itself to real-time data collection during the testing operation. Wireline testing includes the necessity to kill the well to convey the wireline tool, which is undesirable, and the short interval that can be tested is frequently unsatisfactory.
Multiple patents exist for reservoir testing using concentric coiled tubing. Reservoir fluid is returned up the innermost layer and well-control fluid is pumped in the outermost layer of the concentric tubing. Sophisticated valves and flow apparatus are required at the surface to maintain well control as the reservoir fluid is diverted into the surface production facilities. The weight and cost of the concentric coiled tubing limits commercial application.
There remains a need for methods and apparatus to test and evaluate reservoirs without having to remove existing completion equipment in the wellbore. There is also a need for methods and apparatus to test and evaluate individual zones within a reservoir including testing of those zones that would not normally flow without artificial lift. Methods and apparatus that may provide a stable amount of hydrostatic lift to a reservoir zone are desired, as well as methods and apparatus for reliably conveying formation fluids from the interior of coiled tubing to the annulus around coiled tubing at some point higher in the string. There is also a need for valve apparatus at the base, or anywhere between the surface and the base of a coil of coiled tubing, and there is a need for data communication to the valve apparatus to find out what is going on at or near the valve apparatus.